Ok I just did the airbox mod on my 03 explorer, I would strongly recommend it.

Basically, the 3rd gen has terrible airflow to the airfilter, just one tiny hole. So what you do is take a drill bit and drill a ton of holes in the lower half of the airbox, which allows more air to be ****** into the engine. I did it and gained about 1 mpg and more low end torque (I would say).